Method for producing a hollow shaft, in particular a camshaft and a camshaft produced according to said method

ABSTRACT

Hollow shafts, and particularly camshafts, are produced using an internal high-pressure forming (IHF) process. Cams and/or machine elements are mounted at intervals onto the outer surface of the hollow shaft, depending on the use of the latter, by a non-positive and/or positive fit, in a position appropriate to their function when the hollow shaft is placed in the forming tool. An element with approximately the same external diameter as the internal diameter of the hollow shaft is placed in at least one of the hollow shaft, and the hollow shaft together with the cams and/or machine elements that have been pushed onto the same and the inserted element are placed in an IHF tool. Once the IHF tool is closed, the medium is caused to act under the required high-pressure in the hollow shaft. At the same time as the medium is acting internally, at least one ram is pressed axially against at least one front face of the hollow shaft. Thus, filling the IHF mould with a material flow induced by the pressure effect of the medium and the mechanical pressure of the ram. The element is thus enclosed by the material of the hollow shaft and the cams and/or elements are connected to the hollow shaft by the non-positive and/or positive fit by means of the expansion of the hollow shaft. The end of the hollow shaft sealed by the element is mechanically machined to suit functional requirements.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to a method of producing a hollow shaft, inparticular a camshaft, according to the internal high-pressure formingprocess (IHF), cams and/or machine elements being mounted on the outerlateral surface of the hollow shaft, in such a way as to be adapted tothe use of the latter, in a frictional and/or positive-locking mannerand so as to be distributed in functionally correct positions. Themachine elements may be, for example, gears, drives, cam plates or thelike. A preferred field of application is camshafts for motor vehicleengines.

(2) Description of the Related Art including information disclosed under37 CFR 1.97 and 1.98

It is known to produce camshafts for motor vehicle engines by theinternal high-pressure forming process (IHF) by a hollow shaft beingwidened by the action of pressure after the cams have been pushed on.Liquids are preferably used as pressure medium. In this case, the camswhich are pushed on are connected to the shaft in a frictional andpositive-locking manner (DE 34 09 541 A1). Even if this process provesto be very effective for mounting machine elements and cams on the shaftand is used in practice, shafts produced in this way still have theshortcoming that, at their ends, functional elements separately producedin a further process have to be connected to the shaft. Bolts areinserted into the shaft with an appropriate snug fit and arefrictionally connected to the shaft by pins. It is also conventionalpractice to weld these bolts to the shaft or to press them into place.These bolts either project from the shaft and are provided with a threadin this region or they have an internal thread.

The general trend in mechanical engineering, in particular in theconstruction of motor vehicle engines, is to reduce the weight with theoutput being at least the same. To this end, the camshafts have for sometime been used as hollow shafts. In this case, the persons skilled inthe art have endeavored to produce these hollow shafts in such a waythat the requisite machine elements are also connected to the hollowshaft in a highly reliable manner and at a low production cost.

There are applications of hollow shafts in which a connection to drivesis necessary at one end or both ends. For this purpose, it is known toconfigure these machine elements in such a way that they are designed asa sleeve which are pushed onto the shaft and fastened. At the outer end,the machine element is designed as a flange, at which the coupling iseffected (DE 38 00 912 A1). In this case, there are shortcomings withregard to the high mechanical production cost for the element, theaccurate fit on the shaft and the frictional connection to the shaft.The connection may also be produced by IHF, but all the shortcomings arenot removed.

It is known to form the ends of the hollow shaft by rotary swaging orupsetting in such a way that a thickness increase takes place, theinside diameter is reduced and the outside diameter, by materialaccumulation, is brought to such a size that a machine element mountedin a known manner is fastened. In this case, the end of the shaft is tobe upset by an IHF process in such a way that a collar or flange isproduced. These process steps can also be carried out by swaging orrotary swaging (DE 197 10 84.8).

All of the known processes for producing elements connected to thehollow shaft for the purpose of coupling or mounting have thedisadvantage in common that the process for producing and for connectingsaid elements to the shaft in a frictional and positive-locking mannerrequires at least one additional process step. In addition to this thereis also the mechanical treatment. For example, joining processes arenecessary and subsequent hardening and/or machining. In addition, amachine fit is required, which in turn increases the cost.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is to configure the method mentioned at thebeginning in a more efficient manner.

According to the invention, this object is achieved according to claim1. Claims 2 to 11 show advantageous configurations of the method. Ahollow shaft produced according to the invention is defined in claim 12;claims 13 to 18 relate to expedient configurations of this hollow shaft.

According to the invention, two processes known per se independently ofone another are combined. The IHF process is applied with the upsettingapproximately at the same time.

Machine elements, e.g. gears and/or cams, are arranged on the hollowshaft in accordance with its function and are pushed onto the hollowshaft into their function-related position. This hollow shaft withcomponents thus pre-fitted is inserted into an IHF tool. In a knownmanner, a plunger is moved in the axial direction at least toward oneend of the hollow shaft with the pressure medium of the IHF tool actingat the same time. As a result, the hollow shaft is widened to arelatively pronounced extent at the locations at which no machineelement is positioned on the outside, whereas, in the region where amachine element is positioned, the latter is connected in a frictionaland positive-locking manner by the internal pressure. At the same time,the hollow shaft with the inserted element is upset by the pressureeffect and by the movement of the plunger in the axial direction, as aresult of which the thickness of the material is increased and theelement is positioned in the hollow shaft in a frictional andpositive-locking manner and thus, due to its form adapted to the use ofthe hollow shaft, serves as a termination of the hollow shaft and as aconnection to other units.

Depending on the geometrical design of the inserted element, thisupsetting causes material of the hollow shaft to be brought in front ofand/or behind said element. The element is thus locked in the axialdirection. If an axially continuous bore is made in the element, thepressure comes into effect on both sides of this element.

In accordance with the use of the hollow shaft, preferably as acamshaft, i.e. its bearing arrangement, connection to correspondingunits of an engine or other drive elements, the element is mechanicallycut off together with the hollow shaft and a plane surface is producedin the process. A bore or a thread, for example, is made in the latter.

In adaptation to the function of the hollow shaft, it is also possiblefor the element, after it has been connected to the hollow shaft, to bemechanically treated in such a way that a bolt or a threaded boltremains. In this embodiment, the element may also already beprefabricated in its shape before being inserted and connected to thehollow shaft.

A further embodiment of the solution is that the element forms a unitwith the plunger of the IHF tool, which acts axially at the same time asthe pressure medium, and projects into the hollow shaft. Aftercompletion of the IHF process, the plunger together with the element iswithdrawn. Depending on the configuration of the IHF tool and of thediameter of the element, the end of the hollow shaft is given the shaperequired for the function. The final size is produced by knownmechanical treatment.

If the element remains in the hollow shaft, the element is locked in theaxial direction, i.e. it is connected to the hollow shaft in africtional and positive-locking manner.

It may also be advantageous to reduce the element in diameter betweenits two ends, as a result of which the connection to the hollow shaft isimproved.

Depending on the intended use of the hollow shaft, it may beadvantageous to cut off the hollow shaft at the end face in the regionof the element after the element has been pressed in, so that a planesurface is produced. The cutting-off is expediently effected by cut-offgrinding. An axially running thread may be subsequently made in thissurface in order to fasten any desired part or machine element.

The advantage of the method according to the invention consists in thefact that two highly productive processes, internal high-pressureforming and upsetting, are combined at the same time in one process withthe use of simple-to-produce machine elements to be connected to thehollow shaft. This results in very short production times.

A further advantage consists in the fact that, due to the method and thespecial configuration of the machine elements, in particular of theelements to be inserted into the hollow shaft, only a very small amountof rework becomes necessary. The hollow shafts produced according to themethod, in particular camshafts for motor vehicle engines, are extremelylight and very cost-effective.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The prior art and the invention are described with reference toexemplary embodiments. In the associated drawings:

FIGS. 1 a and b show embodiments of the ends of a hollow shaft accordingto the prior art,

FIG. 2 shows a partial section through an IHF tool with inserted hollowshaft,

FIGS. 3 a to 3 c show an embodiment of a hollow shaft with a firmlyinserted element,

FIG. 4 shows a partial section through a hollow shaft with insertedelement and mounted cam, and

FIG. 5 shows an embodiment of an end of the hollow shaft without anelement remaining in it.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a and 1 b show how an end of a hollow shaft is producedaccording to the prior art. In the region of one of its ends, the hollowshaft 1 is treated according to a swaging process known per se or alsoby upsetting in such a way that, with a constant outside diameter D_(A)of the hollow shaft 1, the inside diameter D_(i) of the hollow shaft 1is reduced to the diameter D_(B) of a bore 2. This means that materialaccumulation is effected in the end region. This upsetting is effectedby heating, hammering or even by another forming process. Either thebore 2 is incorporated during this process and then has to bemechanically reworked, or the end of the hollow shaft 1 is completelyclosed and the bore 2 or a thread 3 is then incorporated after themachining of the end face.

The method according to the invention is described with reference toFIG. 2. Inserted into a known IHF tool 4 is a hollow shaft 1, theoutside diameter D_(A) of which corresponds to the inside diameter ofthe tool 4. At the same time, an element 5 whose outside diameter D_(E)is slightly smaller than the inside diameter D_(i) of the hollow shaft 1is inserted into the hollow shaft 1 at a predetermined point. The tool4, which is in two pieces as a rule, is closed. A plunger 6 of the tool4 is moved axially under high pressure, with a pressure medium acting inthe hollow shaft 1 at the same time, so as to press against the end faceof the latter. In the process, the material of the hollow shaft 1 isupset in such a way that the element 5 is enclosed by the material ofthe hollow shaft 1 to such an extent that the previous inside diameterD_(i) of the hollow shaft 1 is reduced to D_(ii). The element 5 is thusconnected under high pressure to the hollow shaft 1 in apositive-locking and/or frictional manner. At a line 7, an end sectionis cut off in a known manner, preferably by cut-off grinding, and aplane surface, in which a thread, for example, is incorporated, isproduced.

Various embodiments of the element 5 are shown in FIGS. 3 a to 3 c.Depending on the effect of the plunger 6 and of the pressure medium andof the geometry of the element 5, the material of the hollow shaft 1 isupset in front of and behind the element 5, and the inside diameterD_(i) of the hollow shaft 1 is reduced to D_(ii). The plunger 6 of theIHF tool presses in the direction of the arrow. In the embodimentaccording to FIG. 3 b, the pressure medium acts on both sides of theelement 5 through the bore 8, although it only penetrates from one side.This embodiment of the element 5 is especially advantageous when theelement 5 is arranged further away from the end of the hollow shaft 1.In FIG. 3 a, the plunger 6 acts on one side and the pressure medium actson the other side in order to obtain the material accumulation.

In FIG. 3 c, the element 5 is of tapered design.

FIG. 4 shows how a machine element 9 or cam is mounted simultaneously onthe hollow shaft 1 in the region of the element 5. According to FIG. 3b, the material is accumulated on both sides. It has surprisingly beenfound that, at this point of the hollow shaft 1, its outside diameter DAis increased and thus the machine element 9 mounted there is connectedto the hollow shaft 1 simultaneously in a frictional and/orpositive-locking manner.

With this example, it is shown how processes previously carried outseparately can be executed in a single IHF process. An advantage of themethod according to the invention results therefrom.

FIG. 5 shows another embodiment of the method. The plunger 6, whichpresses axially at the same time as the pressure medium acts, is firmlyconnected in its front part to the otherwise separate element 5, i.e.the plunger 6 is designed as element 5′ on the front side. The materialflow resulting during the method, during the thickness increase orupsetting, is limited on the inside by the element 5′, the outsidediameter of which ≦ the inside diameter of the hollow shaft 1, and thusmaterial is brought locally outward but also inward in front of theelement 5′. Unlike the examples of FIGS. 2 to 4, the complete plunger 6,5′ is removed from the hollow shaft 1 after completion of the IHFprocess. However, by appropriate design of the element 5′ and of the IHFtool, the plunger 6 may also be connected to the hollow shaft 1 in africtional and positive-locking manner and is mechanically separatedfrom the element 5′ after completion of the process.

The elements 5 and machine elements 9 or cams are produced in a knownmanner in a preceding process.

1. A method of producing a hollow shaft according to an internalhigh-pressure forming process (IHF), cams and/or machine elements beingmounted on the outer lateral surface of the hollow shaft, in such a wayas to be adapted to the use of the latter, in a frictional and/orpositive-locking manner and so as to be distributed in functionallycorrect positions, wherein the cams and/or machine elements required forthe function of the hollow shaft, when the hollow shaft is inserted atthe point and position related to the function, are pushed onto thehollow shaft and positioned; an element having approximately the sameoutside diameter as the inside diameter of the hollow shaft ispositioned in at least one end of the hollow shaft; the hollow shaft,with the cams and/or machine elements pushed onto it and with theinserted element, is inserted into an IHF tool; after the IHF tool hasbeen closed, a medium under the requisite high pressure in the hollowshaft is brought into effect; at the same time as the medium acting frominside, at least one plunger is pressed axially against at least one endface of the hollow shaft in order thus to fill the IHF mold by thematerial flow caused by the pressure effect of the medium and by themechanical pressure of the plunger, as a result of which the element isenclosed by the material of the hollow shaft, and the cams and/ormachine elements are connected to the hollow shaft in a frictionaland/or positive-locking manner by the widening of the hollow shaft; andin that that end of the hollow shaft which is closed by the element ismechanically treated in accordance with the function of the hollowshaft.
 2. The method as claimed in claim 1, wherein the plunger actingaxially against the end face of the hollow shaft, at its end directed inthe direction of the hollow shaft, is designed in such a way that, afterthe completion of the IHF process, a defined recess is produced astermination of the hollow shaft by the withdrawal of the plunger.
 3. Themethod as claimed in claim 1, wherein a plane surface is produced at theclosed end of the hollow shaft by mechanical treatment and an internalthread or a bore is incorporated in this plane surface.
 4. The method asclaimed in claim 1, wherein a bolt or a threaded bolt is made on theelement.
 5. The method as claimed in claim 3, wherein the elementinserted into the hollow shaft has already been given the approximatefunction-related form in a preceding mechanical process and is processedaccording to the IHF process so as to be true to size and compatiblewith the function.
 6. The method as claimed in claim 1, wherein themachine elements, cams and elements are produced in a separate process.7. The method as claimed in claim 1, wherein that end of the hollowshaft which is produced by the IHF process is mechanically reworked onthe inside and/or outside.
 8. The method as claimed in claims 1, whereinthe hollow shaft, after the IHF process, is cut off in the region of theinserted element by a machining process, preferably by cut-off grinding,in such a way that a plane surface is produced.
 9. The method as claimedin claim 8, wherein bores and threads are incorporated in the planesurface.
 10. The method as claimed in claim 1, wherein the machineelements and/or cams and/or elements are produced from a materialdifferent from that of the hollow shaft.
 11. The method as claimed inclaim 2, wherein the IHF tool, in a defined region of the end of thehollow shaft to be produced, is increased in its inside diameter so thatthe outside diameter of the hollow shaft is increased in this region bythe material flow.
 12. A hollow shaft produced as claimed in claim 1,having cams and/or machine elements which are attached to the hollowshaft as a function of the use of the hollow shaft and which, on thehollow shaft widened by internal high-pressure forming, are frictionallyconnected to the hollow shaft in such a way as to be compatible with thefunction, characterized in that the hollow shaft is closed on at leastone side in a frictional and/or positive-locking manner by an element,and in that the element is processed in such a way as to be adaptedgeometrically and mechanically to the function of the hollow shaft. 13.The hollow shaft as claimed in claim 12, wherein the element has a boreor an internal thread.
 14. The hollow shaft as claimed in claim 12,wherein the element is designed as a bolt, pin or threaded bolt on itspart extending over the hollow shaft.
 15. The hollow shaft as claimed inclaim 12, wherein the element is a solid bolt and is provided with aphase at least on one side.
 16. The hollow shaft as claimed in claim 12,wherein the element has an axially continuous bore.
 17. The hollow shaftas claimed claim 12, wherein the element has a reduced diameter in aregion between its two ends.
 18. The hollow shaft as claimed in claim12, wherein the element is tapered in its outside diameter toward oneend.
 19. The method claimed in claim 1 wherein the hollow shaft is acamshaft.
 20. The hollow shaft claimed in claim 12 wherein the hollowshaft is a camshaft.